Indicator



C. J. FITCH July 26, 1960 INDICATOR 2 Sheets-Sheet 1 Filed Jan. 28, 1957INVENTOR CLYDE J. FlTCH his ATTORNEYS C. J. FITCH July 26, 1960INDICATOR 2 Sheets-Sheet 2 Filed Jan. 28, 1957 CURVE A CURRENT VSPOTENTIAL OF MERCURY DROP.

CURVE B SURFACE TENSION CURVE 0F MERCURY DROP.

mm K T N mJ m M m 2% I hls FIG. 4.

. reference to. the drawings,

Unit d St e Pats 2,946,954 INDICATOR Clyde J. Fitch, Endicott, N.Y.,assignor to International corporation of New York I 3 EiledJan. '28, 1957, Ser. No. 636,616

2 Claims. (Cl. 324-97) Business Machines Corporation, New York, N.Y., a

was 2,946.9 t

Patented July 26, 1960 c 2 ganic plastic or glass, is provided with atightly fitting cap 11 which may be joined. to the casing with cement,by welding, or by another type ofsealed joint. A cathode 12 is formed bya wire which is embedded in the cap 11. The cathode 12 is wetted in themercury at the lower end and holds a drop of mercury thereon. The cellchamber 17 is divided into two portions, a cathode chamber 17 and acommunicating anode portion 17", separated by a dam 18. Within the cellchamber 17' is a solution of an electrolyte 20, which may for example bean aqueous 7 solution of an inorganic salt as described in greater de-Another object is to provide a visual indicator which may be operated ona voltage of the order of 1 to 3 volts and therefore may beadvantageously used, in transistor circuitsl 5 7 Still another object ofthe invention is to devise a visual indicator which is utilized. 7

The visual indicator'of the present invention comprises an electricalcell having a chamberinwhich there are designed to 'hold and retain aliquid. The cell chamber also contains'a drop of a second liquid, suchas mercury, which is insoluble in the first liquid. The drop is adaptedto be held by surface tension on the cathode. When an electricalpotential V is applied across 'the anode and cathode, or whentheintensity of the potential is changed, this produces a change in thesurface tension of the drop, thereby causing the mercury drop to changeits position on the cathode. A light source is mounted on one side ofthe cell, which is adapted to pass light through the cell in apredetermined path. The light path is so disposed that the movement ofthe drop of liquid, responsive to the change in potential, changes theamount ,of light from the light source which passesin the light path. Bythe arrangement described, the change in light intensity may be observedor measured as an indication of the change in potential applied acrossthe cathode and anode.

compact and maybe economically .35 mounted an anode and a cathode, thechamber being Since the change in surface tension, with the resultingchange in the position of the drop, may be made responsive to lowvoltages of the order'of' l to 3 volts, it follows that the electriccell-type device described may be used as a visual indicator forelectrical pulses in low voltage circuits such as transistorizedcircuits.

The invention, maybe understood. more fully by considered together withthe following description /1 1 a I Figure l is a front elevation'view ofthe indicator cell; Figure 2 is a side elevation view of the cell insection taken in a plane indicated by the line 2--2 on Figure l andlooking in the direction of the arrows;

Figure 3 shows an assembly of several of the cells and how a singlelight source may be used for all; and

Figure 4 is a graph illustrating the performance characteristics of aparticular electrolytic cell.

Referring first to Figures 1 and 2 which illustrate certain structuralfeatures'of the cell per se and of its operation, a cell casing 10,which may for example be ortail hereinafter. A positive electrode oranode 21 extends through the cap 11 and is embedded therein. On one sideof the cell is a source of light 25- which is transmitted through aclear Lucite window 25. The casing 10 should be opaque. A window 27 isformed in the opposite side of the casing 10 and light from the source25' passing through the cell 9 emerges through the window 27 to betransmitted to a viewer by a, Lucite rod 28. In dotted lines at 3 1there is indicated the position of the mercury drop when the electricalpotential is such that the surface tension of the mercury drop 16 hasbeen decreased, causing the mercury drop to fall to the position.indicated, still, however, retained by cathode 12. Preferably, thecylindrical light path is small enough, and the mercury drop 16 is largeenough, so that in the lower position 31, the mercury drop completelyobstructs the path 30. An observer at 32, therefore, may readilyintensity of the light in the path 30.

The liquid 20 may bea solution of an electrolyte and preferablysuch asolution that will not cause gas to evolve at the electrode when anelectrical potential is applied. If an electrolyte 'is used which willproduce appreciable amounts of gas, then a suitable vent adjacent theroof of the cell, not shown inthe drawings, is provided. Preferably sucha vent is ofsmall dimensions, so as to prevent the escape of liquidwhile still permitting the escape of gas. Preferably a wetting agent isadded to the aqueous solution to decrease its surface tension andthereby increase the difierence in surface tension between the cellliquid-and the mercury drop. An. example of an electrolyte solutionwhich may be used in indicator cells is as follows;

G. Potassium chloride 50.0 Disodium phosphate p 30.5 Citric acid 2.5p-Quinone 0.02.5 -Hydroquinone 0.025 Triton NE 1 0.05

Distilled water to make one liter. (.pII=7.1-7.4)

1 An and alkyl polyether alcohol. 7 .Non-aqueous highly polarizedorganic solvents, such as N,N-dimethylformamide containing quaternaryammonium salts, also might be employed for the electrolyte. Thecontainer used with these solvents must be of a mateprial, such asglass, that will not be attacked or dissolve into the solution.

The sizejandmaterial of the cathode wire are of significance in that thesize will have a bearing on the'locatio n of the upper 'and lowerpositions of. the mercury he's'ize'of'the mercury drop '1s'"ofimportancesince the action'of the indicator cell'hinges on thebalancefbetween the weight .ofthe mercury and its surface tension; thatis,"t'he higher the surfacetens'ion the higher thefposition the mercurywilltendto assume in 'itsraisedpo'sition,

whereas the greaterth'e 'weight of the dropthedowerfthe position'themereury'will tend to"as'sume inits raised position. 'With a"0.02'5 inchdiameter wire cathode, it has been-found that a satisfactory size forthe mercury drop is'0.052 gram, which corresponds with a dropdiameter of0.07l-inch. 'It ispreferred that the cell be. constr ucted so thatthe-lowermost end of the cathode wire will just touch the top of themercury drop when the latter is resting on the bottom of the cell. "Withan 'OLZS-inch diametercathode wire cut 01f square anda mercury drophavinga weight of 0.052 gram, thelower end of the wire should bespacedabout 0.055-0062inch from the bottom of thegcell, In the-cell shown inFigures. 1. and .2, the cathode portion 17';-of-the-ce1l is0.106inchtFig. l) by 0.125 'inch (Fig; 2) by 0.150 inch-high, and thedistance of' the lowercnd of the cathodefrom the bottom of the'cell-chamb'er is;0;055 inch,- whiletheother dimensions are to scale.With this construction, themercury in measured ainoimt and "the cellliquid may be added to the .cell

through an aperture -not shown,- afterwhich the aperture is sealed. 'Themercurythen will fall tothe bottomof the 'ell-= and form a" drop which'will be in contact with the lower end ofthe cathode soas to bepickcd upand'held f by thecathode, generally-in the-raised position, when thereisno 'potential applied across the cell.

InFigure '4 -there is illustrated graphically thecurrent i'nr'n'i'c'rc'iantper'es (shown as the ordinate) which maybe produced bythe applic'ation'of a'given'potential: in volts s1r6wn a's' 't heabscissa) between the anode and cathode bf acll', using an 1 aqueouselectrolyte of: the type exem- 'plified above. The-latter relationshipis shown in curve Abf -Figure 4. Curve B, shown as' a broken line,represents a typical surface tension -ve'rsus voltage relationship forthe mercury drop. The higher points on the parabolic "surface tensioncurve will produce an elevated position of i'the drop,"whereas-the-lower points representrconditions "under" which themercury drop"will assume uthe vflower J'position'on the cathode. --Itwill A be notedtrout-Figure 4 th'at atzero'potentialthere-will-be a-finitecurrentthrough mate range -15 to -/-2.25 volts, including the 1 volt bias. Thecurrent leakage corresponding with the voltage range indicated will besubstantially less than 100 microamperes, generally about 5 to 20microamperes.

Although in the specific illustration of the indicator cell of theinvention the signal was produced by interruption of the path of light,byzzthermercury drop, if desired the signal may be produced by lightreflected from, rather than interrupted by, the mercury drop, namely, byviewing the drop.

Figure -3 illustrates antassembly "of indicator cells;o,f the type shownin detail in Figures-.1.- and 2. .With this assembly a singlesource oflight will sufi'ice for a plurality of cells. The cells maybe arrangedto represent a number or a group of numberspr any otherrequiredinformation.

Although specific embodiments of the invention have been describedherein, it will be apparent to those skilled in the. art thatthere aremany modifications and equivalents withinthescope ofthe'teachir 1g ofthe-application. Accordingly, it is intended that allsuch modificationsand equivalents .be included within the scope ofthe appended claims.

""I claim:

"1. A voltage indicating electrolytic cell comprising an enclosingcasing of non-conducting material enclosing a .cell chamberfilled withliquid capable of conducting an electric current, afirst electrodeformed of conducting .material extending through ,said non-conductingcasing and having its inner efid in contact with ,saidliquid, said.inner endhavinga .drop of mercury suspended. erefrom and held thereonby. surface. tension, a second electrode .alsoextending through.saidnon-conducting. casing and into contact with said liquid butmounted out of ,contact 'with said first .electrode, .said chamberhaving afloorpor- ..tion:ad aptec l to:hold said drop adjacenttolsaidinner end of said first electrode, the distance between thebottom of -.-the.first-.electrodevand said floor being less thantheverintheipresence of the electrolyte. The potential corresponding with azero current is about 1 volt. Accordingly, the indicator celloftheinventionnix-preferably biased with-a negative charge of about 1 volton the.cathticalldiameter .oflthe drop, so that-the first electrode will=-touch-and 'pick up the. drop whenthe, drop is resting on esaid'fioor,:a light source on onessideof said celladapted to ;pass .light throughthe .cell in. a predetermined, path so 'disposed that movement.of.-saidpdrop .will change the sarnount of light from said tsource passilg through said cell 2. TThezcell :as' :describedzin claim .1 .in'which.the first :electrode is :thercathode; the second electrodefis theanode,

and thie liquid is agpolar electrolyte solution.

"zReferences-(lited-in the file of this patent UNITED "STATES PATENTSCurtis Aug. 9, 19-32 .Hindle Jan. 2, .1934 .Coleman Mar. 14, 19441,821,361 1,942,027 -..2,s43,sss

Arrhenius, published by Longmans,'Green andCo, New

York, 1902, pages 232, 233-relied on.

